Two bats are going for their midnight feed.
After an hour or so, one bat gets tired of looking and goes home with no blood.
The other bat comes home with blood dripping from its mouth. The first bat says enviously, "Where did you get all that blood from?"
The second bat replies, "Follow me. I'll show you."
After awhile the second bat leads them to a cave. He says, "You see that wall over there?"
The hungry bat excitedly says, "Yes!"
Other bat says, "I didn't."